CVE-2026-67422: pymdown-extensions: Exponential-backtracking ReDoS in caret, tilde, betterem, and magiclink inline processors

Vulnerability summary

CVE-2026-67422 is a high (CVSS 7.5) vulnerability in facelessuser pymdown-extensions. EPSS estimates a 0.61% chance of exploitation in the next 30 days, higher than 49.1% of scored vulnerabilities.

Timeline

1. 06-08-2026
   PublishedVulnerability first disclosed.
2. 07-08-2026
   Last modifiedVulnerability information updated.

Description

pymdown-extensions is a collection of extensions for the Python Markdown library. In versions up to and including 11.0, four inline processors (caret, tilde, betterem, and magiclink) use regular expressions whose content groups can partition a run of delimiter characters in exponentially many ways, causing catastrophic backtracking. As a result, a single untrusted Markdown line under 50 bytes rendered with markdown.markdown() in each extension's default configuration drives the rendering thread into unbounded CPU usage that grows exponentially with input length, enabling an unauthenticated remote attacker who can submit Markdown to cause denial of service. The exposure is concrete for web applications that render user-supplied Markdown (comments, wikis, issue bodies, live preview), including any app using pymdownx.extra which bundles the vulnerable betterem default, as well as hosted docs/CI systems that build untrusted Markdown. The issue has been fixed in version 11.0.1.

• CWE-1333Inefficient Regular Expression ComplexityThe product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.